A lithium-ion battery (LIB) is a type of rechargeable battery that is widely used in various applications due to its very high energy density compared to other rechargeable battery types. LIBs are commercially available in portable electronics, power tools, electric vehicles, and many other devices.
Commercially available LIBs are generally designed to be charged and discharged at room temperature. Such consumer-targeted LIBs also are designed to safely discharge down to a cut-off voltage of around 2.5-3.0 V.
It is known to use LIBs to power medical implants, such as ventricular assist devices (VADs). Unlike consumer-use LIBs, the LIBs used in medical implants are designed to be charged and discharged at body temperature (around 37° C.). Also, medical implant LIBs typically are designed to discharge down to close to 0 (zero) V. This low cut-off voltage capability for implantable LIBs is a safety feature to protect the LIBs from over-discharge conditions which can damage the LIB cell and lead to its failure.
Although commonly used, LIBs present certain safety hazards. LIBs are particularly susceptible to abuse, which can lead to thermal runaway. Abuse can be external physical abuse, such as puncture, compression, dropping, vibration, or exposure to heat or fire. Abuse can also result from internal causes like over-charging, over-discharging, high rate charge at low temperature, or high or low temperature operation.
Thermal runaway refers to a situation where an increase in temperature causes a further increase in temperature, leading to a dangerous chain reaction. In such conditions, temperatures may quickly rise to unsafe levels, creating a potentially destructive result such as an explosion or fire. Thermal runaway can result from an internal fault, either from improper use or raw material defects.
To prevent dangerous conditions and explosions, consumer LIBs generally have vents, which allow the cell to release excess internal pressure. In the event of an abusive situation, the vents can release vapors of the cell's organic solvent electrolyte. Unlike consumer LIBs, the LIBs for use in implantable medical devices are hermetically sealed and have no vents, due to the damage that would be done to the body if vapors or organic solvent electrolytes escaped from the cell.
For life-sustaining medical devices, battery failure could lead to catastrophic results. For any battery implanted in the body, a battery explosion could do significant harm to the user. Some batteries known in the art are capable of measuring temperature to determine that a fault has occurred. But for critical devices like VADs, once a fault has occurred, it may be too late to mitigate the disastrous health effects.